A Skin-Deep Dinosaur Issue

A. Presumably, said Mark A. Norell, chairman of the division of paleontology at the American Museum of Natural History. But not all at once.

“Since we can’t directly observe extinct animals, we need to look at close relatives,” Dr. Norell said. “Birds are living dinosaurs, crocodilians their closest relatives. Both shed skin in patches and strips, not entire skins like snakes.

“Because crocodiles and birds share a common ancestor, we predict this skin-shedding style was present in that ancestor,” he continued. “Nonbird dinosaurs descend from this same ancestor. Without other information, we predict that even giant dinosaurs exfoliated their dead dry skin in patches.”

Everything that has skin sheds it, Dr. Norell emphasized, but there is a tremendous diversity in how skin sheds. In humans, for example, rubbing the dry skin of an arm across something black leaves a white scuff of dead skin cells, he said. And in birds, skin dries and sloughs off as small patches, like peeling after a bad sunburn.

Reptile shedding usually conjures visions of whole snakeskins, shed as a continuous piece, “looking like the ghost of a living serpent,” Dr. Norell said. But this is an anomaly; most animals do it differently. Typical reptiles — lizards, crocodiles and turtles — shed dry, irregular skin patches, and that is probably how dinosaurs did it, he said.

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